1. Field of the Invention
The present invention relates to a hybrid toner for use in an electrostatic electrophotographic developing system and a method of preparing the toner. More particularly, the invention relates to a hybrid toner that has particles having a core-shell type structure, that prevent a toner blocking phenomenon and image contamination that are caused by the dispersion of waxes or colorants onto the surface of the outer layer of toner particles. The toner prepared according to the method of the invention provides improved storage characteristics of the toner.
2. Description of the Related Art
In an electrophotographic process or an electrostatic recording process, a developer used to form an electrostatic image or an electrostatic latent image may be a two-component developer, formed of toner and carrier particles, or a one-component developer, formed of toner only. The one-component developer may be a magnetic one-component developer or a nonmagnetic one-component developer. Plasticizers such as colloidal silica are often added independently into the nonmagnetic one-component developer to increase the flowability of the toner. Generally, coloring particles obtained by dispersing a colorant, such as carbon black, or other additives in a binding resin are used in the toner.
Methods of preparing toner include pulverization or polymerization methods. In the pulverization method, toner is obtained by melting and mixing synthetic resins with colorants and, if needed, other additives, pulverizing the mixture and sorting the particles until particles of a desired size are obtained. However, in a dry pulverization process, when an amount of wax included is greater than about 2.5 weight %, the durability and storage stability of toner decrease. Therefore, increasing the amount of wax in order to prevent offset and improve fixation of toner onto paper is undesirable. In addition, when toner is prepared using a pulverization method, it is inevitable that wax becomes embedded in the surface of the toner and protrudes outwardly during the pulverization step. This causes what is referred to as a toner blocking phenomenon, resulting in low image quality and poor storage stability of the toner.
Meanwhile, in a polymerization method, a polymerizable monomer composition is manufactured by uniformly dissolving or dispersing a polymerizable monomer, a pigment, a polymerization initiator and, if needed, various additives such as a cross-linking agent and an antistatic agent. Next, the polymerizable monomer composition is dispersed in an aqueous dispersive medium which includes a dispersion stabilizer using an agitator to shape minute liquid droplet particles. Subsequently, the temperature is increased and suspension polymerization is performed to obtain polymerized toner having coloring polymer particles of a desired size. In particular, there is a method of preparing a toner by forming core particles using a vinyl-based monomer and an initiator, and then forming a core-shell by polymerizing a vinyl-based monomer having the same hydrophilic property as that of the core particles and a higher glass transition temperature (Tg) than that of the core particles. However, in order to maintain the structure of the core-shell and improve the storage of toner, the core-shell has to be thick.
In particular, in electronic photocopiers, laser beam printers, electrostatic recording apparatuses or the like in which images are formed using electrophotography, electrostatic recording or the like, toner used to develop an electrostatic image requires a developer for fixation of toner onto paper at a low temperature required for high speed devices.